br Although killed whole cell

2019-05-15

Although killed, whole-cell oral cholera vaccines (OCVs) have been known to be efficacious since 1986, and the bivalent whole-cell vaccine Shanchol has been licensed in India since 2009, OCV was not regarded as useful for controlling cholera outbreaks until recently. Many public health officials questioned the use of OCV, including concerns about its cost, the feasibility of undertaking large campaigns, the acceptability of OCV among vaccinated communities, and the possibility of diverting resources from other interventions. There was also uncertainty as to whether the vaccine, although known to be effective in endemic countries (eg, India or Bangladesh), would be effective in areas without a history of cholera, such as Haiti. When the cholera epidemic started in Haiti, Shanchol was not yet prequalified by WHO, and only a limited supply was available, so FRAX597 of large numbers of people was not realistic. Assuming effectiveness in Haiti, and if the vaccine had been available and had been used earlier, computer models suggest it could have averted many cases and deaths.
Although cholera vaccine was not used in the first two main waves of the epidemic, pilot projects were done in 2012 to deliver Shanchol to about 100 000 people in urban and rural Haiti. Subsequently, the Ministry of Health undertook larger campaigns in 2013, and plan to implement additional OCV campaigns in the coming years. Furthermore, the Ministry of Health has included the use of OCV in its national strategy for elimination of cholera, along with a continuing effort to improve water and sanitation. The earlier reports showed that OCV was acceptable and that OCV campaigns were feasible in Haiti, but a new report by Louise Ivers and colleagues in provides important new information, showing that the vaccine\'s effectiveness in Haiti is comparable to that found in endemic countries of Asia and Africa. Of 47 people with cholera, 33 (70%) self-reported vaccination versus 167 (89%) of 188 controls (vaccine effectiveness 63%, 95% CI 8–85). Conversely, there was no association between self-reported or verified vaccination and non-cholera diarrhoea (vaccine effectiveness 18%, 95% CI −208 to 78 by self-report and −21%, −238 to 57 by verified vaccination).
Similar efficacy and effectiveness of the two killed OCVs—Dukoral and Shanchol—has been documented. The two vaccines differ in that Dukoral is more expensive and is administered in a glass of buffer solution to preserve the B subunit component of the vaccine, which increases the logistic requirements for its use. By contrast, Shanchol, which has no B subunit, needs no buffer, is less costly, and consists of only 1·5 mL liquid, which can be consumed directly from a vial. Shanchol is now available through the OCV stockpile, which is supported partly by the Global Alliance for Vaccines and Immunization. It is being used primarily as a response to an outbreak, but it will probably also be used for groups at risk in endemic areas. Clearly, much work is needed to identify how best to use the vaccine in a manner that maximises its cost-effectiveness.
Some of the limitations of this study are related to the small sample size, which is a common problem in cholera effectiveness studies and which limits the ability to discern differences among subgroups. In this study, the point estimates differed in some subgroup comparisons (eg, age group and time since vaccine administration), but the sample was not powered to identify whether these differences were real. Ivers and colleagues were also not able to assess the potential for herd protection, which was found in other studies. Although OCV protects vaccinated individuals, it also lowers the risk for unvaccinated neighbours if vaccine coverage is sufficiently high. Modelling work predicted that 50% coverage could avoid transmission in endemic areas. Thus, further studies are needed to better understand how to maximise the effect of herd protection.